This invention relates generally to a hydraulic latching spool valve and more specifically concerns a valve having a latching chamber formed in the interior of an elongate movable piston. The latching chamber is in fluid communication with the supply pressure to the valve and has an area exposed to the supply pressure that generates sufficient latching force to overcome opposing forces and latch the valve in the open position after an initial pulse of open fluid pressure.
Hydraulic valves are used in a variety of applications to control flow in hydraulic circuits. While pilot operated poppet valves have been employed for many years, recent changes in control system design have rendered traditional poppet valves less than optimal. With traditional valves, hydraulic pilot pressure is applied and maintained in order to open the valve and keep it in an open position. A poppet valve that was designed for use in a traditional hydraulic system is disclosed in U.S. Pat. No. 5,901,749 assigned to Gilmore Valve Co., the assignee of the present invention. The valve disclosed in this patent requires constant pilot pressure to stay open. If pilot pressure unintentionally drops for any reason, the valve will close because of spring force. This sometimes results in the unintentional closure of a valve.
Maintaining a constant pilot pressure to keep the valve open has a number of drawbacks.
Any hydraulic system can be troubled by leaks, and keeping a valve under constant pilot pressure may be difficult if there are leaks in the system. Further, maintaining constant pilot pressure requires energy. Thus, control systems have shifted to a design in which pilot pressure need only be pulsed in order to open the valve, and then released. There is, therefore, a need for a valve design capable of latching in the open position after only a brief pulse of pilot pressure. The term xe2x80x9cpulsedxe2x80x9d as used herein means that a pilot is opened and pressurized fluid is directed to a desired apparatus, for example the present invention, for 2 to 3 seconds, and then the fluid is vented and pressure falls to zero psi.
A previous attempt to address this need can be found in U.S. Pat. No. 6,209,565, however the device described suffers from several problems. For example, the device is needlessly complicated. It uses two pistons, i.e. the pilot open piston and a second piston (called a head) in the latching piston assembly. Two moving pistons require additional seals that increase the potential for leakage and failure. There is, therefore, a need for a simple, elegant valve that does not require constant pilot pressure in order to keep it in an open position.
The present invention provides a simple valve design that is able to remain open without constant pilot pressure, and that minimizes the risk of leakage due to the fluid pressure holding the valve open. Briefly, the present invention is a hydraulic latching spool valve which is adapted to be inserted into a valve chamber in a body. Some end users of the hydraulic latching spool valve have bodies that receive the valve and others do not. Therefore the hydraulic latching spool valve may be sold with or without a body. The valve body defines a supply port, a function port, a vent port, a pilot close port, and a pilot open port. The supply port is connected to a pressurized fluid source which delivers supply pressure to the spool valve. The pilot close port is connected to a close pilot to deliver close fluid to the spool valve when the close pilot is pulsed. The pilot open port is connected to an open pilot to deliver open fluid to the spool valve when the open pilot is pulsed.
The spool valve itself comprises a valve cage, a seal assembly carried by a moveable elongate piston, a spring, a pilot open chamber, a pilot close chamber, and a latching chamber. The valve cage is sized and arranged to be inserted into the valve chamber of the body. The valve cage defines an upper circular seat positioned between a valve supply port and a valve function port, and a lower circular seat positioned between the valve function port and a valve vent port. The seal assembly is carried by an elongate moveable piston. The piston moves from a closed position, in which the seal assembly is engaged with the first seat and disengaged with the second seat, to an open position, in which the seal assembly is engaged with the second seat and disengaged with the first seat. The spring is positioned within a chamber in fluid communication with the pilot close port and urges the piston into the closed position. The pilot open chamber is in fluid communication with the pilot open port and serves to retain fluid that exerts pressure on the head of the piston, causing the piston to move from a closed position to an open position where the piston is actuated.
The latching chamber is formed within the interior of the elongate moveable piston and is in fluid communication with the supply pressure when the valve is in the open position. The latching chamber has an area exposed to the supply pressure that generates sufficient latching force to overcome the opposing forces generated by the spring and the supply pressure acting against the piston. Thus, when the open pilot is pulsed, the elongate moveable piston moves to the open position and supply pressure fills the latching chamber. The piston is then held in the open position until the close pilot is pulsed, which added pressure combines with the pressure exerted by the spring to force the piston into the closed position. These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.